The invention relates to a valve solenoid comprising a coil and a an iron circuit, which are arranged in a housing which can be employed in areas endangered by explosion.
Such valve solenoids have long been known and are evident, for example, from the German utility model 90 03 343 or from the U.S. Pat. No. 5,138,292.
Widely varying types of ignition protection are known. Types of ignition protection in accordance with IEC or EN (EN 50014 ff.) are: xe2x80x9cpressure-resistant encapsulation (EExd)xe2x80x9d, xe2x80x9cenhanced safety (EExe)xe2x80x9d, xe2x80x9cover-pressure encapsulation (EExp)xe2x80x9d, xe2x80x9cintrinsic (EExi)xe2x80x9d, xe2x80x9coil immersion (EExo)xe2x80x9d, xe2x80x9csand filling (EExq)xe2x80x9d and xe2x80x9ccast encapsulation (EExm)xe2x80x9d.
Designs for explosionproof solenoids are also known in which it is not only the xe2x80x9cpurexe2x80x9d ignition protection types mentioned above which are used but also combinations of these ignition protection types, such as the ignition protection types xe2x80x9ccast encapsulationxe2x80x9d combined with xe2x80x9cenhanced safetyxe2x80x9d or xe2x80x9cpressure-resistant encapsulationxe2x80x9d combined with xe2x80x9cincreased safetyxe2x80x9d .
The object of the invention is to provide an explosionproof valve solenoid that can easily be manufactured at low cost while satisfying the ignition protection type xe2x80x9cpressure-resistant encapsulationxe2x80x9d in the region where external cables are connected.
This object is achieved according to the invention, in a valve solenoid of the type described above, in that the coil and the iron circuit are embedded in a casting compound introduced into a housing part, which casting compound prevents an explosive atmosphere reaching live parts and is simultaneously used for fixing purposes and electrical insulation (cast encapsulation). Connecting elements of the coil are arranged in a housing part which withstands internal pressure in the case of an explosion and prevents transmission of the explosion to the environment (pressure-resistant encapsulation).
The major advantage of dividing the housing into two housing parts, one of which satisfies the xe2x80x9ccast encapsulationxe2x80x9d ignition protection type and the other the xe2x80x9cpressure-resistant encapsulationxe2x80x9d ignition protection type is that the coil and the iron circuit, in particular the solenoid enclosure sleeve, are not part of the pressure-resistant area. This housing part does not therefore require complicated fitting procedures, which are necessary in the case of pressure-resistant encapsulations because of the fact that the gaps must not allow ignition penetration. The physical size of the solenoid can, in addition, be reduced by the avoidance of such gaps, which must have a specified minimum length.
In addition to its ease of manufacture, such valve solenoids also have the advantage that cast encapsulated coils and iron circuits or solenoid enclosure sleeves are available as standard parts with the result that stockholdings are reduced. Nevertheless, the external cables can be connected in a pressure-resistant, encapsulated area arranged in the second housing part.
Further advantages and features of the invention are the subject matter of the following description and of the drawing representation of an embodiment of the invention.